What does HTTP/2 mean for a reverse proxy server?
How HTTP/2 affects the implementation of a proxy server? Especially, for example, when a client sends an HTTP/2 request to a content server that only supports HTTP/1.x, should the proxy server tranform the HTTP/2 request to HTTP/1.x request before directing the client request to the content server? And upon receiving response from the content server, should the proxy server transform the response to the HTTP/2 format before sending it back to the client?
Answer
As dsign discussed, your understanding is correct.
However I thought it was worth pointing out there are still massive advantages to HTTP/2 at your edge connection (i.e. Your reverse proxy) as the issues HTTP/2 solves (primarily latency) are less of an issue over the typically shorter, typically high bandwidth hop from the reverse proxy to the content server.
For example if you have a 100ms delay to the reverse proxy at the edge and only 1ms delay between the reverse proxy and the content server, then the fact the content server is speaking HTTP/1.1 to the proxy server probably won't have much impact on performance due to the super fast 1ms latency. So the end client (speaking HTTP/2 to the reverse proxy) still sees a massive performance boast over HTTP/1.1.